Experimental study of mixed convection heat transfer in a vertical channel with a one-sided semicylindrical constriction with prescribed heat flux

An experimental study of mixed convection heat transfer is carried out in a vertical channel with a one-sided semicylindrical constriction with prescribed heat flux while the other bounding walls are insulated and adiabatic. The semicylinder is placed horizontally at the mid-plane with a blockage ratio (BR, ratio between the semicylinder diameter and the thickness of the rectangular section) of 0.3 and a semicylinder aspect ratio (AR, ratio between the length and diameter of the semicylinder) of 6. The effect of opposing buoyancy on the flow and thermal behavior is analyzed for fixed Prandtl number of Pr = 7, Reynolds number based on semicylinder diameter of 20 <= Re <= 350 and buoyancy strength or modified Richardson number, Ri* = Gr*/Re-2, from 20 to 350. For relatively large values of Ri*, flow visualization images and thermal analysis confirm the presence of a complex three-dimensional (3D) two-vortex structure with two recirculation bubbles present at the forebody and rear of the semicylinder. Surface temperature distributions and averaged Nusselt number at different Reynolds and modified Richardson numbers have been obtained. The results show that variation of the local temperature distributions with angular position and spanwise location become evident, and their relation to the presence of a complex 3D vortex structure that develops close to the semicylindrical constriction has been studied and discussed in detail. Moreover, empirical correlations for the overall Nusselt number are obtained using both Re and Gr* and Re and Ri* as the controlling parameters. (C) 2017 Elsevier Inc. All rights reserved.